Selectable() render into AutoFitPadding only when full-fitting (fix aac99819)

Columns: mouse dragging uses absolute mouse coords. Fixed dragging left-most column of an auto-resizable window. #125

Active column (when dragged) not clipped so it can release its active state (extends 16ddd796)

Fixed C4267 size_t to unsigned int conversion warning.

Fixed hovering over a popup's child (popups disable hovering on other windows but not their childs) #197

Examples: GLFW Set modifier key state by inspecting imgui's io.KeysDown array (see #183)

Fix outdated documentation

Otherwise a change in layout moving active widget to a clipped region
may lock the active id.

DragFloat() latch value internally, allows finer control, honor precision settings, slow step with integer works #180

DragFloat() latch value internally, allows finer control, honor precision settings, slow step with integer works #180